1. Field of the Invention
The present invention relates to separation of liquid mixtures, and in particular to a method and apparatus for separating small quantities of a liquid having a low boiling point dispersed within a large quantity of immiscible liquid having a higher boiling point.
2. Description of the Prior Art
Efficient separation of emulsified liquid mixtures is necessary in a wide range of industrial environments. For example, the lubricants employed in equipment such as gas or air compressors combine with large volumes of water during operation, necessitating disposal of the entire liquid effluent. Because the effluent is considered hazardous waste due to the relatively small amount of lubricant present therein, the ability to separate the bulk liquid into hydrocarbon and liquid fractions permits restriction of expensive disposal measures to the hazardous material itself. In addition, pre-treatment of contaminated water prior to purification frequently benefits from initial separation of hydrocarbon fractions.
Reliable techniques for separating small quantities of hydrocarbons dispersed within a large quantity of immiscible liquid are few, and the apparatus which presently perform this function provide limited efficiency. There are three types of conventional methods/apparatus for oil-water separation: (a) gravity oil-water separators; (b) dissolved air flotation; and (c) chemical treatment, in accordance with L. K. Wang et al (44.sup.th Purdue Industrial Waste Conference Proceedings, p. 655-673, 1990)
Typical gravity oil-water separators, for example, commonly employ grease-traps, baffles, skimmers and/or polishing filters to promote separation. Because they operate without phase changes, these systems require large quantities of energy for separation of free oils from the oil-water mixture, and typically cannot separate emulsified mixtures.
Dissolved air flotation is frequently used for further separation of oils from the oil-water mixture which has been previously treated by conventional oil-water separator. Chemical(s) may or may not be used.
Oil-water separation apparatus capable of operating on emulsions ordinarily utilize one or more emulsion-breaking chemicals for chemical treatment, in which either dissolved air flotation or gravity sedimentation can be used for clarification. In general chemical treatment results in production of waste sludge that poses a solid-waste disposal problem.
The limitations associated with these oil-in-water systems derive from the respective physical properties of oil and water. The specific heat constant and heat of vaporization of water are much larger than those of typical organic compounds, including oils. Most oils boil at a higher temperature than that of water, however. Systems that rely on any form of distillation therefore require considerable energy input in order to raise the temperature of the mixture of 100.degree. C. or above, because the overall specific heat of the mixture will be close to that of water; in addition, a further quantity of energy must be applied to induce boil-off of the water.
By contrast, systems designed to remove small quantities of water from large amounts of oil require significantly less energy; this is due to the lower specific heat of the mixture (which will be closer to that of the oil), as well as to the smaller absolute amount of water that must be vaporized. Furthermore, such systems typically operate at a lower temperature than oil-in-water systems in order to minimize boil-off of organic compounds along with the water; such boil-off is rarely observed with with oil-in-water system.
Volatile organic compounds (VOCs), semi-volatile organic compounds, and many other hazardous organics frequently contaminate surface water and ground water supply sources. Table A presents a partial list of toxic organic substances, their health effects, boiling points (BP), maximum contamination levels (MCL), and contamination sources. For water pollution control, collection of any liquid containing these toxic organic substances for proper disposal is now an important environmental engineering task.
The method and apparatus of this invention can be effectively applied to separation of these toxic organic substances from a contaminated liquid mixture, based on their different boiling points. For instance, methylene chloride (BP=40.1.degree. C.) can be easily separated from a contaminated water (BP=100.degree. C.) containing methylene chloride, when the liquid temperature is controlled at 42.degree. C. to vaporize methylene chloride while keeping a bulk of water in liquid form, in accordance with the present invention utilizing the improved heat transfer, nebulization, condensation and heat pump technologies.
TABLE A __________________________________________________________________________ ORGANIC CONTAMINANTS HEALTH CONTAMINANT EFFECTS BP .degree.C. MCL mg/l SOURCES __________________________________________________________________________ Benzene Cancer 80.1 0.005 Fuel (leaking tanks), solvent commonly used in manufacture of industrial chemicals, pharmaceuticals, pesticides, paints and plastics. Carbon Possible Cancer 76.74 0.005 Common in cleansing agents, tetrachloride industrial wastes from manufacture of coolants. p-Dichlorobenzene Possible Cancer 173.70 0.075 Used in insecticides, moth balls, air deodorizers. 1,2-Dichloroethane Possible Cancer 83.50 0.005 Used in manufacture of insecticides, gasoline. 1,1- Liver/Kidney 47-49 0.007 Used in manufacture of plastics, Dichloroethylene Effects dyes, perfumes, paints, SOCs. Methylene Toxic by 40.10 NA Used in removing paints, chloride inhalation, aerosol spraying, solvent ingestion and skin degreasing, plastic processing, absorption. solvent extraction. 1,1,1- Nervous system 75.00 0.140 Used in manufacture of food Trichloroethane effects wrappings, synthentic fibers. Trichloroethylene Possible cancer 86.70 0.005 Waste from disposal of dry (TCE) cleaning materials and manufacture of pesticides, paints, waxes and varnishes, paint stripper, metal degreaser. Vinyl chloride Cancer risk -13.90 0.001 Polyvinlychloride pipes (PVC) and solvents used to join them, industrial waste from manufacture of plastics and synthetic rubber. Total Cancer risk Primarily formed when surface trihalomethanes water containing organic matter Chloroform 61.20 0.1 is treated with chlorine. Bromoform 151.20 0.1 __________________________________________________________________________
Several systems have been developed for removing small quantities of water entrained within a heavy hydrocarbon, such as oil.
U.S. Pat. No. 235,521 issued to E. Fox on Dec. 14, 1880, describes a method of securing the separation of the aqueous matter or other impurity from the liquor proper, which consists in spraying the crude spirit upward by a jet of heated fluid, to give the proper direction to the lighter vapors, and thus promote their separation by gravity, exposing the liquid in a thin film upon a large extent of surface for the spirit-vapors to separate as the liquid runs down, and conveying these separated spirit-vapors upward and to a condenser, substantially as set forth. Fox's invention (U.S. Pat. No. 235,521) also relates to a distilling or rectifying apparatus which is the combination of a containing-vessel, plates or screens in the upper part thereof, a supply-tube for the crude spirit, vertical jet-tubes for the heated fluid that atomizes the liquid and vaporizes the spirit, a filtering-diaphragm above the plates or screens, and a pipe to the condenser, substantially as set forth.
U.S. Pat. No. 3,608,279 issued to R. W. West on Sep. 28, 1971, describes an apparatus for separating fatty acid distillates entrained in steam. The gaseous mixture is introduced into a vessel under temperature and vacuum pressure conditions that promote separation.
U.S. Pat. No. 4,197,190 issued to A. Foster on Apr. 8, 1980, discloses a process for dehydrating tars and hydrocarbon oils containing water, wherein such material is heated prior to being sprayed into a holding vessel. Separate outlets are provided for removing the separate components, and the water component is also scrubbed prior to release.
U.S. Pat. No. 4,789,461 issued to Clare et al on Dec. 6, 1988, describes a system wherein heavy crude oil containing water is sprayed onto a pool of heated oil that has been dehydrated; the water evaporated upon contact with the pool is evacuated through a vent.
The foregoing systems (U.S. Pat. Nos. 235,521, 3,608,279, 4,197,190 and 4,789,461), designed primarily for separating small quantities of water from large samples of oil, exhibit a number of disadvantages. These would be magnified if applied to an oil-in-water mixture. Because none provides any mechanism for intrasystem temperature maintenance, a large amount of energy must be introduced by external equipment to ensure that the temperature of the mixture at the point of separation remains at or above the distillation temperature; an oil-in-water system would require significantly greater energy input. All four of the foregoing systems also utilize spray nozzles to introduce the mixture into a separation vessel. Although spraying tends to break surface tension and thereby promote separation of the components, the utility of this technique is limited by the amount of mechanical shear that may be introduced. Furthermore, it has been found that use of spray nozzles at the temperatures necessary for efficient oil-in-water separation results in "searing," a phenomenon whereby the interior of the vessel becomes coated with solid material that acts as an unwanted insulation layer and interferes with heat transfer. The present invention relates to oil-water separation or liquid-liquid separation using the techniques of mainly recycled gas heating, nebulizing, gravity separation of high-boiling-point liquid, vaporization of low-boiling-point liquid, and condensation of low-boiling-point liquid, and aiming at energy recycle and reuse.
The process of treating hydrocarbon oils, is disclosed by C. B. Forward in his U.S. Pat. No. 1,189,083, issued Jun. 27, 1916. Forward's patent discloses a new technology involving atomizing the oil under controlled pressure with a heated vapor into the open interior of a chamber; then driving off the combined vapors and the unvaporized products through separate channels from said chamber, the said channels being kept under restrictions to maintain a vapor pressure in the chamber of seventy-five pounds and upward and to prevent vapor from escaping through the channel for the unvaporized products. Forward's invention also relates to the process of treating crude petroleum oil by superheating the oil and atomizing the same under controlled pressure into a chamber with a volume of heated vapor, and then separating the volatized from the unvolatized products in said chamber under a pressure with a minimum of about seventy five pounds maintained therein. Specifically, a steam boiler is used to generate the heated steam vapor, and an oil heater is used to heat the crude oil. Both the heated vapor and the heated crude oil meet together inside a separator through an atomizer. The present invention does not involve the use of a steam boiler nor an oil heater for oil-water separation. Specifically, when the present invention is applied to oil-water separation the oil-water mixture is not preheated by an oil heater and the inert gas, such as air (instead of steam vapor) is used for nebulization (instead of atomization) of the oil-water mixture. In the nebulization process of the present invention, the inert gas pretreated with the make-up heat as well as the recycled heat in pool liquid mixes, heats, and distributes the incoming, previously unheated oil-water mixture at the nebulizer forming a mist for separation of small amount of oil from a bulk of water vapor. In the atomization process of Forward's invention, the steam vapor generated by a steam boiler mixes with the preheated crude oil at the atomizer, forming aerosols for purification of crude oil. Furthermore, in the present invention, the water vapor is the liquid with low-boiling point to be separated or to be removed from the influent, while in Forward's invention, the water vapor is specifically produced for purification of the high-boiling-point crude oil.
The method and apparatus for liquid evaporation below ebullition point is disclosed by H. E. LaBour in his U.S. Pat. No. 1,493,756 issued May 13, 1924. Specifically, LaBour's invention relates to an improved method of and means for causing evaporation below the ordinary ebullition point, and for de-alcoholizing beer at such a relatively low temperature that the flavoring of the beer is not destroyed. LaBour's process of treating a fluid material for removing therefrom a volatile constituent, comprises moving a definite, constant charge of gas in a completely closed circuit of fixed volume, at one point in the circuit projecting the fluid to be treated in the form of a substantially complete fluid to be treated in the form of a substantially complete fluid curtain, deflecting the fluid downwardly away from said curtain, passing the gas upwardly through said fluid curtain and away from said deflected body of fluid, the gas picking up the volatile constituent in the form of a vapor, at another point in the circuit cooling the gas to condense out the volatile constituent, at another point in the circuit reheating the gas for repeated passage up through said fluid curtain, between said cooling point and said reheating point imparting an impelling force to the gas so as to maintain a relatively low pressure at the cooling point and a relatively high pressure at the reheating point, said completely closed circuit maintaining said charge of gas in an unvarying body against the introduction of atmosphere or extraneous gases and out of contact with liquid washes, whereby the volatile flavoring constituents of said fluid material are retained in said charge of gas. LaBour's invention does not relate to nebulization, which is the heart of the present invention.
The method for removing tetranitromethane from commercial trinitrotoluene is disclosed by R. H. Gartner in his U.S. Pat. No. 1,632,959, issued Jun. 21, 1927. Gartner's invention comprises atomizing commercial liquid trinitrotoluene by means of a nonreactive hot gaseous stream, subjecting the clouds thus produced to hot nonreactive gaseous streams until the tetranitromethane is vaporized, then subjecting the trinitrotoluene to cold non-reactive gaseous streams by which the trinitrotoluene is solidified, and then withdrawing the hot gases from the presence of the solidified trinitrotoluene. Again Gartner's invention does not relate to nebulization, which is the heart of the present invention.
The method for separating finely divided animal and vegetable fibers, such as the lint of wool, cotton, and linen waste, from lubricating oils is disclosed by T. W. Potter et al in their U.S. Pat. No. 1,709,230 issued Apr. 16, 1929. Their invention is particularly intended to be employed as a means of renovating oil coming from used journal-box waste. Specifically, the method of Potter et al for separation of lint and foreign matter from used journal-box oil comprises preheating a quantity of said oil to vaporize water therein, transferring the oil to a tank closed to the atmosphere and in communication with a condenser, applying heat and controlling the pressure in said closed tank to heat the oil therein to substantially complete vaporization without cracking to leave said lint and foreign matter on the bottom of said closed tank, and allowing the vaporized oil to condense in said condenser. In operation, both impure oil and steam are injected into a preheater from where the mixture of the preheated impure oil and steam flows to a heating tank to where additional steams is further added for complete vaporization. The totally vaporized oil is carried by the steam to a condenser from where the condensed oil is purified and collected, and the residual steam is discharged. The present invention, however, does not relate to vaporization of oil using steam.
The process of purifying used crank case oil, particularly from automobiles, so as to remove coloring matter and light hydrocarbons therefrom, and to raise the viscosity and lower the carbon content is described in U.S. Pat. No. 1,823,185 issued Sep. 15, 1931 to D. S. Belden. By means of Belden's process, one is able to accomplish these objects under conditions by which the fire hazard is greatly reduced. Briefly stated, Belden's process comprises mixing used crank case oil with from 1% to 30% by weight of a finely divided clay adsorbent, preferably of the acid-activated type, distilling the light components from such mixture while assisting the volatilization by bubbling through the mixture a lively stream of inert gas, such as CO.sub.2 or nitrogen, stopping the distillation when the light constituents have been removed and then filtering the residual oil from the clay. Belden's best mode of process operation for purification of used lubricating oil comprises: mixing said oil with a clay adsorbent; heating said mixture to approximately 600.degree. F., while bubbling therethrough a lively stream of inert permanent gas; distilling the lighter fractions from said oil and condensing them in an inert atmosphere; separating the condensate from the inert gas; and returning the latter eventually to a batch of oil and adsorbent under distillation. The present invention does not relate to: purification of a hydrocarbon oil, such as crank case oil by distillation; inert gas bubbling through said oil; and condensation of purified oil. Instead the present invention relates to: heating gas with recycled and make-up energy; nebulizing the oil-water mixture with the preheated gas; forming the mist; settling the high-boiling-point liquid by gravity; and discharging the waste steam resulting from the low-boiling-point liquid.
Prior method and apparatus for purifying liquids, or for rendering non-aqueous liquids such as mineral hydrocarbon oils anhydrous, free from dissolved gases, volatiles and volatile hydrocarbons which result from oxidation is described in U.S. Pat. No. 2,047,157 issued Jul. 7, 1936 to C. J. Rodman et al. The process of Rodman et al for removal of moisture and gases from non-aqueous liquids comprises introducing an inert gas into the liquid, spraying the liquid and contained gas in finely dispersed form in a vacuum to separate moisture and gases therefrom, introducing an anhydrous, gas-free adsorbent material into the liquid, filtering and adding inert gas to the filtered liquid, the process being effected out of contact with water and atmospheric gases. The process of Rodman et al for rendering non-aqueous liquids anhydrous and gas-free comprises feeding the liquid onto a rapidly rotating member in a closed system to cause the liquid to be impelled centrifugally in film-like form of substantially 1 millimeter thickness while continuously maintaining in the system a vacuum adapted to cause substantially instantaneous evaporation of moisture and gases from the liquid and while excluding air and extraneous moisture from the system, continuously removing from the system moisture and gases liberated from the liquid, and recovering substantially anhydrous and gas-free liquid. The present invention, however, relates to: gas heating with the make-up and recycled energy; nebulizing the gas-liquid blend with an improved nebulizer; gravity settling the high-boiling-point liquid; vaporizing the low-boiling-point liquid; etc. for liquid-liquid separation.
U.S. Pat. No. 3,326,778 issued to A. E. Mock on Jun. 20, 1967 describes a novel process involving the rapid passage of dry gas, preferably air, at extremely high temperature through an enclosure body of impure water whose surface is exposed to a gas environment of relatively high pressure, with the temperature of said impure body being maintained just below its boiling point for said environmental pressure even though the temperature of the air rapidly passing therethrough is substantially higher than said boiling point. In Mock's invention, the air is saturated with water vapor which in turn can be extracted by condensation, and the temperature of the impure body is maintained below its boiling point by adding impure water to the body as well as withdrawing concentrated impure water therefrom. The major components of Mock's invention includes: a flash evaporator, an air furnace, a steam boiler, a condenser and a pure water reservoir, which combined extract pure water from impure water, such as sea water. The present invention does not involve the use of Mock's major process components.
U.S. Pat. No. 4,289,589, issued to W. Koehler et al on Sep. 15, 1981 describes a process for separating toluene diisocyanate and/or higher boiling solvents from distillation residues obtained from the phosgenation of toluene diamine in the presence of solvents wherein the separation takes place in a fluidized bed at temperatures of 140.degree. C. to 280.degree. C. The invention of Koehler et al discloses mixing a liquid with a gas, and distilling. This prior art is made of record not relied upon. The present invention relates to mainly liquid-liquid separation by nebulization.
A process for purifying a C.sub.4 and/or C.sub.5 hydrocarbon cut containing water and dimethyl ether as impurities is disclosed by L. Asselineau et al in their U.S. Pat. No. 4,474,647 issued Oct. 2, 1984. Specifically, the C.sub.4 and/or C.sub.5 olefinic hydrocarbon cut, containing dimethyl ether and water as impurities, in a relative proportion of dimethyl ether to water of at most 5:1, is purified in a distillation zone where it is introduced at an intermediate level, distant from the top or from the bottom thereof by at least 3 theoretical plates, optionally with a stripping gas, and separated into a overhead fraction comprising an aqueous liquid phase and a hydrocarbon liquid phase at least partially recycled as reflux to the upper part of the distillation zone, and a bottom fraction formed of the purified C.sub.4 and/or C.sub.5 olefinic cut. The major process components of their invention include: a distillation column, a settler, and a condenser. The present invention does not involve the use of a distillation column, a settler and a condenser, and relates to mainly nebulization for liquid-liquid separation.
Still another method and apparatus for the separation of oil from water in an emulsion thereof is disclosed by H. B. Grow in his U.S. Pat. No. 4,477,356 issued Oct. 16, 1984. Grow's invention relates to inducing the oil-water emulsion into an elongated chamber at a temperature below the boiling point of water; recirculating a portion of the emulsion oil through the chamber at a boiling temperature well below the refining temperature of the oil; drawing off the product oil from the chamber end remote from said induction end thereof; and drawing off the water by-product as steam from the chamber above a controlled liquid level of emulsion-oil therein, waste heat from the product and by-product being conserved. The present invention has same application, but totally different operational principles and apparatus.
U.S. Pat. No. 4,666,587 issued to C. K. Martin, May 19, 1987 describes a process for recovery of a finished oil product from crude or waste oil contaminated with water and the like by heating the waste oil in a tank with a heating flame which may be gas or oil fired. In Martin's process, the waste oil is heated until vapors including light ends and the desired finished oil product are produced from the waste oil within the tank. The vapors are introduced into the heating flame so that additional heat is developed by such afterburning to heat the waste oil in the tank. The finished oil product as recovered from the waste oil is discharged from the tank by a suitable outlet pipe arrangement. The present invention relates to nebulization of a liquid-liquid mixture for their phase separation, thus is different.
A by-pass oil refining device for an internal combustion engine is disclosed by L. H. Sims in his U.S. Pat. No. 4,717,474 issued Jan. 5, 1988. Sims' apparatus is equipped with an atomizing nozzle that constricts oil flow from a solid contaminant filtering element to a vaporization chamber where liquid contaminants are vaporized. The atomizing nozzle has a constricting orifice which is of a diameter sufficiently large to allow recirculation of oil to the vehicle engine, but which is small enough so that oil from the filtering element entering the vaporization chamber is atomized into a mist. Atomization of the oil significantly increases the extent to which liquid contaminants are vaporized and removed. The present invention relates to liquid-liquid separation by nebulization (instead of nozzle atomization).
Still another apparatus and method for using a heated waste gas stream to evaporate a volatile component such as water or a solvent from a liquid solution is shown in U.S. Pat. No. 4,734,159 issued Mar. 29, 1988 to T. F. Korenowski. Korenowski's invention comprises a flue to feed the gas stream from the source of heated gas; a container having an inner chamber to hold the liquid for evaporation of the volatile compound and an outer chamber connected to the flue which forms a gas channel substantially surrounding the inner chamber through which at least a portion of the gas stream flows to supply heat to the inner chamber and evaporate the volatile component of the liquid solution; an inlet to feed the liquid solution into the inner chamber; upper and lower liquid level sensors to control the quantity of liquid solution fed into the inner chamber to establish a liquid level therein; a sparger for agitating the liquid solution in the inner chamber; a sump below the container and connected to the flue to receive any condensate from the gas stream and any liquid leaking from the inner chamber; an outlet to combine, vent and discharge the evaporated volatile component from the inner chamber and the gas stream from the outer chamber; and an outlet for removing the liquid from the inner chamber. While the present invention's application is also evaporation of a low-boiling-point liquid such as water from a liquid mixture, the present invention's apparatus and method is totally different.
U.S. Pat. No. 4,946,559, issued to Kroneld et al in August 1990 and U.S. Pat. No. 4,402,711 issued to Stellacid et al in September 1983 are representative of processes in which liquid components are separated by systems employing processes related to the present invention, in which various techniques for maintaining temperature and pressure control of, gas contact chambers, pumping operations related to liquid level control, and recycling of the higher boiling point for heat exchange purpose are also employed. However, neither U.S. Pat. No. 4,946,559 nor U.S. Pat. No. 4,402,711 suggests the compressing of feed gas of this invention; U.S. Pat. No. 4,402,711 merely uses fuel gas or superheated steam and U.S. Pat. No. 4,946,559 merely vaporizes a part of the liquids to be separated as feed gas.
U.S. Pat. No. 2,765,917 issued to Francis et al in October 1956 and U.S. Pat. No. 1,968,614 issued to Novotney et al in July 1934 are made of record for recited concern with mixing chamber level control and used of recycling separated components correlated with heat exchange in processes employing heating.
Although the prior art is replete with patents reciting using compressors to facilitate heat recovery from vaporized products of separatory apparatus, U.S. Pat. No. 4,713,089 issued to Robbins in December 1987 and U.S. Pat. No. 4,698,136 issued to El-Allway in October 1987 are made of record; such prior art is generally concerned with stripping or counter current distillation systems and does not suggest the recited use of gas compression in combination with a preheating means, a nebulizer, and a condensation means.
A U.S. invention relating to separation of liquid mixtures, and in particular to a method and apparatus for separating small quantities of a liquid having a high boiling point (such as oil) dispersed within a large quantity of immiscible liquid having a lower boiling point (such as water), was filed by Roland E. Webber, Lawrence K. Wang, and John J. Pavlovich on Oct. 18, 1991 Ser. No. 07/778,778). The present invention is a continuation-in-part of said Oct. 18, 1991 invention by Weber et al Ser. No. 07/778,778). Specifically the present invention relates to separation of liquid mixtures and in particular to a method and apparatus for separating small quantities of a liquid having a low boiling point (such as methylene chloride) dispersed within a large quantity of immiscible liquid having a higher boiling point (such as water).